This invention relates to pipeline transportation systems, and more particularly to a system for the transportation of cargo in containers through a pipeline via hydraulic propulsion of the containers through the pipeline.
Reference may be made to such U.S. Patents as Nos. 3,325,222, 3,328,089, 3,333,901, 3,339,984, 3,556,604 and 3,633,976 disclosing systems of the above-mentioned type, referred to as hydraulic capsule pipelining (HCP) systems.
In such systems, means is provided for pumping a carrier liquid, usually water, through a pipeline, the flow of the liquid being utilized to propel the cargo-carrying containers, which are referred to as capsules, through the pipeline. The containers or capsules, which are generally of elongate cylindrical shape, travel endwise through the pipeline, the diameter of each capsule generally being 5-10% smaller than the internal diameter of the pipe. Each capsule may be provided with a collar, as disclosed in U.S. Pat. No. 3,633,976, to cause the capsule to move in a "nose-up" position at a small angle of attack to increase the hydrodynamic lift on the capsule, thereby providing for lifting the capsule (the density of which is generally greater than that of the waer or other carrier liquid) up off the bottom of the pipeline to increase the velocity of the capsule and decrease the energy loss along the pipe. Under optimum conditions, the capsule moves at a speed slightly greater than the mean flow velocity of the carrier liquid.
In view of the requirement of a hydraulic capsule pipelining system that the capsules must pass relatively freely through the pipeline, the pumping of the carrier liquid through the pipeline has presented serious problems. The requirement is satisfied only by the provision of a special pump in the line capable of having capsules pass therethrough one after another, or the provision of a pumping system which the capsules may by-pass in their travel through the line. Prior special pumps and by-pass systems for the purpose have presented special problems. Thus, the special pump shown in U.S. Pat. No. 3,325,222, which has been referred to as the vortex pump, while quite simple and quite capable of freely passing the capsules, has low efficiency and low pump head. It is understood that the best efficiency obtained to date for this pump is only 15% with a corresponding head of only a few feet for each pump. Another special pump proposed for the purpose, referred to as the rotary-vane pump, comprises a rotor having compartments (between vanes) for receiving capsules exiting from one section of a line and entering the capsules in another section of the line, with provision for delivery of carrier liquid from a centrifugal pump to the rotary-vane pump and discharge of carrier liquid from the rotary-vane pump to the inlet of the centrifugal pump. This, however, has the disadvantage of being bulky (e.g., it has to be made forty feet in diameter to handle capsules fifteen feet long). By-pass systems such as shown in U.S. Pat. No. 3,339,984 have the disadvantage of requiring rapid opening and closing of valves, which causes undesirable large surges of pressure in the pipeline.